1. Field of Invention
The present invention relates to a selective one-way wrench and, more particularly, to a selective one-way wrench that is easily switchable between two modes for transmitting high torque.
2. Related Prior Art
As disclosed in U.S. Pat. No. 1,957,462, a conventional ratchet wrench includes a body member 20, a toothed wheel 24, a pawl 25, a plunger 41, a spring 42 and a manipulator 46. The body member 20 includes a handle 21 extending from a head 22. The head 22 includes two recesses 23 and 26 in communication with each other. The toothed wheel 24 is rotationally placed in the recess 23. The toothed wheel 24 is formed with a non-cylindrical portion 34 for insertion in a socket so that the socket is rotatable together with the toothed wheel 24. The pawl 25 is movably placed in the recess 26 and formed with two pairs of teeth 40 on a side and two recesses 44 separated from each other by a protuberance 45 on an opposite side. The pairs of teeth 40 are for engagement with the toothed wheel 24. A selected one of the recesses 44 receives an end of the plunger 41, which includes an opposite end biased by the spring 42. The manipulator 46 is formed with a cylindrical portion 47 inserted in the pawl 25. There is a key 55 formed with an end inserted in the pawl 25 and an opposite end inserted in the cylindrical portion 47 of the manipulator 46 so that the pawl 25 is rotatable together with the manipulator 46. By manipulating the manipulator 46, the ratchet wrench is turned between two modes. In the first mode, the plunger 41 is inserted in the first recess 44. The first pair of teeth 40 is engaged with the toothed wheel 24. The handle 21 can be pivoted in a first direction to rotate the toothed wheel 24 via the head 22 and the pawl 25. The toothed wheel 24 cannot be rotated as the handle 21 is pivoted in a second direction opposite to the first direction because the first pair of teeth 40 is disengaged from the toothed wheel 24. In the second mode, the plunger 41 is inserted in the second recess 44. The second pair of teeth 40 is engaged with the toothed wheel 24. The handle 21 can be pivoted in the second direction to rotate the toothed wheel 24 via the head 22 and the pawl 25. The toothed wheel 24 cannot be rotated as the handle 21 is pivoted in the first direction because the second pair of teeth 40 is disengaged from the toothed wheel 24. This conventional ratchet wrench however suffers a serious drawback. It fails to transmit large torque in the first or second mode since the spring 42 is inadequate to keep the plunger 41 in the first or second recess 44 to keep the first or second pair of teeth 40 engaged with the toothed wheel 24. That is, it fails to tighten a nut on a screw or release a tightened nut from a screw.
As disclosed in Taiwanese Patent Publication No. 289994, another conventional ratchet wrench includes a body member 10, a toothed wheel 20, a pawl 30, a switch 41 and a spring 44. The body member 10 includes a handle 12 extending from a head 11 that includes a substantially crescent cavity between and in communication with two substantially circular cavities. The toothed wheel 20 is rotationally placed in the first circular cavity. The pawl 30 is a crescent element formed with a slot 32 and movably placed in the crescent cavity. The switch 41 includes a root 42 formed on a lower face, a recess 43 defined in the root 42, and a groove 45 defined in the lower face. The root 42 is placed rotationally in the second circular cavity. The spring 44 includes a helical portion, a first rectilinear portion 441 extending from the helical portion parallel to the axis of the helical portion, and a second rectilinear portion 442 transversely extending from the first rectilinear portion 441. The helical portion of the spring 44 is placed in the recess 43. The first rectilinear portion 441 of the spring 44 is placed in the groove 45 to avoid rotation of the spring 44. The second rectilinear portion 442 of the spring 44 is inserted in the slot 32. The switch 41 is maneuvered to switch the ratchet wrench between two modes. In the first mode, the pawl 30 is moved to a first end of the crescent cavity by the switch 41 via the spring 44. In the second mode, the pawl 30 is moved to a second end of the crescent cavity by the switch 41 via the spring 44. There is however lag in the movement of the pawl 30 by the switch 41 via the spring 44 as the second rectilinear portion 442 of the spring 44 is movable along the slot 32 because the length of the slot 32 is much larger than the diameter of the second rectilinear portion 442 of the spring 44.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.